Diarrhea caused by strains of pathogenic E. coli has been found to be associated with the production of a variety of enterotoxins. Some pathogenic E. coli enterohemorrhagic produce enterotoxins that are closely related to the shiga toxin associated with Shigella-caused dysentery. The first member of the family of shiga-like toxins (SLT) to be isolated was cytotoxic for African Green Monkey (Vero) cells and was originally called verotoxin. Since its structural similarity to shiga toxin has been established by sequencing of the relevant genes, this toxin is now more commonly called shiga-like toxin I (SLTI). See, for example, Calderwood, S. B., et al., Proc Natl Acad Sci USA (1987) 84:4364-4368; Jackson, M. P., et al., Micro Pathog (1987) 2:147-153; Strockbine, N. A., et al., J Bacteriol (1988) 170:1116-1122.
Additional members of the SLT family have subsequently been isolated that can be distinguished serologically, on the basis of gene sequence or host specificity (Gannon, V. P. J., et al., J Gen Microbiol (1990) 136:1125-1135; Weinstein, D. L., et al., J Bacteriol (1988) 170:4223-4230; Ito, H., et al., Microb Pathog (1990) 8:47-60; Head, S. C., et al., FEMS Microbiol Lett (1988) 51:211-216; Schmitt, C. K., et al., Infect Immun (1991) 59:1065-1073; Scotland, S. M., et al., Lancet (1985) ii:885-886; Oku, Y., et al., Microb Pathog (1989) 6:113-122. Various types of SLTII have been described and have been assigned various designations depending on the strain of E. coli from which they are isolated and the hosts they inhabit. Thus, variants have been designated SLTII; vtx2ha; SLTIIvh; vtx2hb; SLTIIc; SLTIIvp and so forth.
All of the SLT's are multimeric proteins composed of an enzymatic (A) subunit and multiple (B) subunits responsible for toxin binding to receptors on host tissues. The binding B oligomers of SLTI, SLTII and SLTIIvh recognize host cell globoseries glycolipid receptors containing at minimum the disaccharide subunit .alpha.Gal(1-4).beta.Gal at the non-reducing terminus; SLTIIvp has been shown to bind to the receptors containing this subunit but not necessarily at the non-reducing end (Samuel, J. E., et al., Infect Immun (1990) 58:611-618; Boyd, B., et al., Nephron (1989) 51:207-210; DeGrandis, S., et al., J Biol Chem (1989) 264:12520-12525; Waddell, T., et al., Biochem Biophys Res Comm (1988) 152:674-679; Lingwood, C. A., et al., J Biol Chem (1987) 262:8834-8839; Waddell, T., et al., Proc Natl Acad Sci USA (1990) 87:7898-7901; Cohen, A., et al., J Biol Chem (1987) 262:17088-17091; Jacewicz, M., et al., J Exp Med (1986) 163:1391-1404; Lindberg, A. A., et al., J Biol Chem (1987) 262:1779-1785.
SLT activity has been detected in stool samples of symptomatic patients (Karmali, M. A., et al., J Clin Microbiol (1988) 22:614-619; Maniar, A. C., et al., J Clin Microbiol (1990) 28:134-135). However, there is difficulty in detecting the presence of SLTs clinically since these are very potent toxins present in low concentrations. In order to assure detection, the SLT present in the sample must be concentrated to enhance the reliability of the assay. Present diagnostic procedures are technically demanding, time consuming and of limited practical use in the clinical setting. Thus there is a clear need for improved diagnostic clinically practical and rapid procedures.
Also, antibiotics are not recommended for treatment of enterohemorrhagic E. coli infection (Robson, W. L. M., et al., J Pediatr (1990) 117:675-676) and the use of antimotility drugs also appears to be counterproductive (Cimolai, N., et al., J Pediatr (1990) 117:676. There is, therefore, also a clear need for new and effective therapeutic agents.
It has now been found that artificial substrates containing the .alpha.Gal(1-4).beta.Gal (P.sub.1 disaccharide) subunit and more preferably the .alpha.Gal(1-4).beta.Gal(1-4).beta.GlcNAc (P.sub.1 trisaccharide) or .alpha.Gal(1-4).beta.Gal(1-4).beta.Glc (P.sub.k trisaccharide) subunit are effective in detecting and neutralizing members of the SLT family under conditions necessary to effect recovery of the patient and as such represent novel therapeutic and diagnostic tools in the treatment of E. coli-mediated dysentery.